Wiper motor

ABSTRACT

A wiper motor has: a magnet disposed on the yoke and formed with at least four poles; an armature disposed on an inner side of the magnet; a speed reduction mechanism unit having an output shaft for transmitting the rotation of the armature shaft; a gear housing connected to the yoke; a gear housing cover covering an opening of the gear housing; a magnet attached to the output shaft of the speed reduction mechanism unit; an absolute position detecting sensor disposed so as to face the magnet; and a control board having the absolute position detecting sensor attached thereto, the control board being disposed between the gear housing and the gear housing cover, and configured to control the rotation of the armature shaft.

CROSS-REFERENCE TO RELATED APPLICATION

This application is entitled to the benefit of and incorporates by reference subject matter disclosed in International Patent Application No. PCT/JP2011/076927 filed on Nov. 22, 2011.

TECHNICAL FIELD

The present invention relates to a motor with speed reduction mechanism.

BACKGROUND ART

In general, in a wiper device to be mounted on a vehicle, a wiper motor is used as a driving source for periodically swinging a wiper arm (see for example Japanese Patent Application Laid-Open Publication No. 2009-189093). This wiper motor has: a motor unit having brushes and an armature; and a speed reduction mechanism unit for reducing the speed of rotation of the armature of the motor unit. The speed reduction mechanism unit is provided with a control device for controlling the rotation of the armature, thereby controlling a position and a speed of the wiper arm. In a wiper motor which can rotate its armature in a forward direction and a reverse direction by using a two-pole magnet and two brushes, since it is necessary to increase the thickness of the yoke on the basis of magnetic flux of the motor unit, there is a possibility of increasing the weight of the wiper motor. For this reason, its inertia is increased. Therefore, there is a possibility of deteriorating the control accuracy of the wiper.

SUMMARY OF THE INVENTION

Therefore, the present invention has been made in order to solve the above-mentioned problems, and an object of the present invention is to provide a wiper motor improved in weight and size, and improved in wiping accuracy.

In order to solve the above-mentioned problem, a wiper motor according to the present invention comprises: a yoke; a magnet formed with four poles in which different magnetic poles are alternately disposed on an inner peripheral surface of the yoke; an armature including an armature shaft which has one end rotatably supported by a bottom portion of the yoke, a commutator which is fixed to the armature shaft, and a core which is fixed to the armature shaft and around which a winding wire is wound, wherein the armature is rotatably disposed on an inner side of the magnet; two brushes slidably contacting with the commutator, the brushes being disposed so as to be spaced apart from each other at intervals of 90 degrees; a speed reduction mechanism unit having an output shaft for transmitting the rotation of the armature shaft by meshing with a worm formed on the armature shaft; a gear housing connected to the yoke, the gear housing being formed with a speed reduction mechanism accommodating part having accommodated therein the speed reduction mechanism unit, and formed into a bottomed open shape; a gear housing cover covering an opening of the gear housing; a sensor magnet attached to the output shaft; an absolute position detecting sensor disposed so as to face the sensor magnet; and a control board having the absolute position detecting sensor attached thereto, the control board being disposed between the gear housing and the gear housing cover, and configured to control the rotation of the armature shaft by using a signal corresponding to the change of magnetic field generated by the sensor magnet and detected by the absolute position detecting sensor.

Furthermore, a wiper motor according to the present invention comprises: a case; a magnet formed with four poles in which different magnetic poles are alternately disposed on an inner peripheral surface of the case; an armature including an armature shaft which is rotatably supported by the case, a commutator which is fixed to the armature shaft, and a core which is fixed to the armature shaft and around which a winding wire is wound, wherein the armature is rotatably disposed on an inner side of the magnet; two brushes slidably contacting with the commutator, the brushes being disposed so as to be spaced apart from each other at intervals of 90 degrees; a speed reduction mechanism unit accommodated in the case, the speed reduction mechanism unit having an output shaft meshing with a worm formed on the armature shaft to transmit the rotation of the armature shaft; a sensor magnet attached to the output shaft; an absolute position detecting sensor disposed so as to face the sensor magnet; and a control board having the absolute position detecting sensor attached thereto, the control board being accommodated in the case, and configured to control the rotation of the armature shaft by using a signal corresponding to the change of magnetic field generated by the sensor magnet and detected by the absolute position detecting sensor.

According to the present invention, since the wiper motor, which can rotate its armature in a forward direction and a reverse direction by using a four-pole magnet and two brushes, is provided with an angle sensor, it is possible to provide a wiper motor improved in weight and size, and improved in wiping accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of a motor with speed reduction mechanism according to one embodiment of the present invention seen from a gear housing cover side;

FIG. 2A is a view of a state in which a gear housing cover is removed from it shown in FIG. 1;

FIG. 2B is a view of a state in which an armature is removed from a yoke in a sectional view of the yoke along a line A-A in FIG. 2A;

FIG. 3A is a fragmentary sectional and development view of the wiper motor shown in FIG. 1;

FIG. 3B is a perspective view of a gear housing cover;

FIG. 3C is a development view of windings of an armature;

FIG. 4A is a view of a state in which a motor unit is removed from the wiper motor;

FIG. 4B is a view of a state in which ;

FIG. 5A is a perspective view of a brush holder part seen from a brush terminal connecting part side;

FIG. 5B is a perspective view of the brush holder part seen from a brush holder side;

FIG. 6 is a view of the wiper motor according to the embodiment of the present invention seen from an output shaft side;

FIG. 7 is a perspective view of a state in which a motor unit is removed from the wiper motor according to the embodiment of the present invention;

FIG. 8 is a view of a state in which a control board is mounted on it shown in FIG. 2A; and

FIG. 9 is a sectional view of a speed reduction mechanism unit of the motor with speed reduction mechanism shown in FIG. 1.

DETAILED DESCRIPTION

A wiper motor 1 as a motor with speed reduction mechanism according to the present invention includes: as shown in FIGS. 1 and 2A, a motor unit 10 for performing a rotating operation with electric current; and a speed reduction mechanism unit 25 for reducing the speed of rotation of the motor unit 10 and transmitting the speed reduced rotation to an output shaft 24.

As shown in FIGS. 1, 2A, and 2B, the motor unit 10 includes a yoke (first case) 13 which is formed into a bottomed cylindrical shape, four magnets 11 are fixed to an inner circumferential surface thereof, a gear housing 26 is fixed to one end surface thereof, and a shaft bearing part 12 is fixed to the other end surface thereof.

Furthermore, as shown in FIGS. 2A and 3A, the motor unit 10 includes an armature shaft 14 having one end rotatably supported by the bearing part 12 and having a worm part 14 a formed at its tip, a commutator 15 fixed to the armature shaft 14, an armature core 16 adjacent to the commutator 15 and fixed to the armature shaft 14, and a winging wire part 17 wound around the armature core 16, wherein an armature 18 is rotatably disposed on the inner side of the plurality of magnets 11. Furthermore, as shown in FIGS. 5A and 5B, the motor unit 10 has a brush holder unit 19 including a plurality of brushes 20 and 20 slidably supporting the commutator 15 with the rotation of the armature 18, and brush holders 21 and 21 holding the respective brushes 20 and 20.

The speed reduction mechanism unit 25 includes a worm wheel part 25 a for reducing the speed of rotation of the motor unit 10, and the gear housing (second case) 26 having a bottomed speed reduction mechanism accommodating part 26 f in which the worm wheel part 25 a is accommodated. Furthermore, the speed reduction mechanism unit 25 further includes a gear housing cover 29 covering an opening of the speed reduction mechanism accommodating part 26 f, and a brush holder accommodating part 26 d in which the brush holder unit 19 is accommodated. The worm wheel part 25 a includes the output shaft 24 for reducing the speed of rotation of the armature 18 of the motor unit 10 and transmitting the speed reduced rotation, and the brush holder accommodating part 26 d is cylindrically formed and is integrally molded with the gear housing 26. The gear housing 26 and the gear housing cover (third case) 29 are fixed to each other by a plurality of screws 40. The wiper motor having an integrated case is constructed by mechanically connecting the yoke (first case) 13, the gear housing (second case) 26, and the gear housing cover (third case) 29 to each other.

The worm wheel part 25 a included in the speed reduction mechanism unit 25 is made of resin such as polyacetal, into a disk shape, and has an outer peripheral surface formed with an engaging part 25 b engaged with the worm part 14 a of the armature shaft 14. The output shaft 24 is integrally mounted at the center of rotation of the worm wheel part 25 a. With this, when the armature 18 rotates, with the rotation of the worm part 14 a, the worm wheel part 25 a engaged with the worm part 14 a rotates with the reduced speed of rotation, thereby reducing the speed of rotation of the armature 18 and transmitting the reduced speed of rotation to the output shaft 24.

To a base end of the output shaft 24 of the worm wheel part 25 a, a cylindrical (button-shaped) sensor magnet 25 c is attached so that its rotation center is axially aligned with the rotation center of the output shaft 24. Furthermore, the sensor magnet 25 c is polarized so as to have: an N pole in a range of 180 degrees in one circumferential direction defined around its rotation center as a center; and an S pole in a range of 180 degrees in the other circumferential direction. In the vicinity of the annular sensor magnet 25 c, a Hall IC for absolute position detection 29 d is provided on a control board 29 c which will be further described below.

As shown in FIG. 9, the Hall IC for absolute position detection 29 d is configured to detect the change of magnetic field generated by the sensor magnet 25 c with the rotation of the output shaft 24, and to convert it into angle data. And on the basis of a signal generated by the Hall IC for absolute position detection 29 d so as to correspond to the change of magnetic field generated by the sensor magnet 25 c, an angle of a current position of a wiper arm on a windshield (not shown) from its specific position such as lower reversing position or stop position of the wiper device attached to the top of the output shaft 24 of the motor with speed reduction mechanism is calculated. The sensor magnet 25 c is integrally fixed to the base end of the output shaft, a swinging member 43 such as wiper arm or motor crank is directly fixed to one end of the output shaft by a fixing member 44 such as nut so as not to move around it, and an intermediate portion of the output shaft 24 is supported by an output shaft support part 26 g formed as part of the gear housing 26 (second case) so as to extend in an axial direction.

Since the output shaft 24 is prevented from being moved in the axial direction by this part, the movement of the wiper arm or the motor crank can be detected with accuracy by the Hall IC for absolute position detection 29 d. Also, since the wiper motor 1 is made up of a four-pole wiper motor, the wiper motor 1 can be reduced in size, and inertia of the wiper motor 1 can be reduced. Therefore, since the loss of the wiper motor 1, such as balance in rotation of the armature 18, is reduced, and responsiveness of control and accuracy of wiping control can be enhanced. Furthermore, since it is not necessary to provide, to the wiper motor 1, a magnet for detecting the rotation of the armature shaft 14 and a sensor for detecting the pole of the magnet, the armature shaft 14 can be reduced in length, and the wiper motor 1 can be reduced in size.

Then, a heat dissipating structure of the gear housing 26 will be described as features of the present invention on the basis of FIGS. 2A, 3A, 6 and 7.

The yoke 13 is integrally molded by press working from a plate material into a bottomed cylindrical shape, and a magnet fixing part 13 a in which the plurality of magnets 11 are fixed onto its inner peripheral surface and a yoke connecting part 13 d integrally connected to the magnet fixing part 13 a are formed in the yoke 13. And in the yoke connecting part 13 d, paired curved parts 13 b and paired flat surface parts 13 c alternately connected so as to be formed into an elliptical shape seen from an axial direction. On the end face of the yoke 13, a flange shaped fixing part 13 e is formed, and the gear housing 26, which will be described further below, is fixed to the flange shaped fixing part 13 e. The yoke connecting part 13 d is formed so that an arc diameter is gradually widened from the magnet fixing part 13 a toward the yoke end face. On the inner peripheral surface of the magnet fixing part 13 a, four magnets 11 are fixed with an adhesive or the like so that two N poles and two S poles, which are different magnetic poles, are alternately disposed, that is, the same poles face each other.

The armature shaft 14 has one end rotatably supported by the bearing part 12 of the yoke 13, and the armature shaft 14 is disposed on the inner side of the four magnets 11. The armature shaft 14 has the other end formed with the worm part 14 a formed into a spiral shape by component rolling.

The armature core 16 is formed into a cylindrical shape by stacking in layers predetermined numbers of core substrates which are stamped out by press working, and the armature core 16 includes a shaft fixing part to which the armature shaft 14 is fixed, and eighteen teeth parts radially extending from the shaft fixing part.

As shown in FIGS. 3A and 3C, a coil 17 a made of copper wire is wound around the armature core 16. One end of the coil 17 a is fixed to the coil connecting part 15 c of one of the segment parts 15 b, and the coil 17 a is wound by lap winding between predetermined teeth parts a plurality of times. Furthermore, after the coil 17 a is wound by lap winding between the predetermined teeth parts the plurality of times, the other end of the coil 17 a is fixed to the coil connecting part 15 c of another segment part 15 b. Then, a connecting line (electric current supply line) 17 b is connected to one segment part 15 b facing another segment part 15 b. In this manner, the coil 17 a is wound around the armature core 16 by repeating a process of winding the coil 17 a about each teeth part. With this, when electric power is supplied to the brushes 20 and 20, electric current flows through the coil 17 a, and the armature 18 is rotated, thereby driving the wiper motor 1.

When the four pole magnet is used, four brushes are normally required. However, in this invention, by connecting facing segments to each other through the connecting line (electric current supply line) 17 b, the electric current flowing through a segment part from one brush 20 flows also through a facing segment part via the connecting line 17 b. With this, the number of brushes can be decreased from four to two.

As shown in FIGS. 5A and 5B, the brush holder unit 19 includes a base part 19 c in which paired curved parts 19 a and paired flat surface parts 19 b are alternately connected so as to be formed into an elliptical shape.

The base part 19 c is formed with an opening portion 19 c 1 through which the armature shaft 14 is penetrated, and a fixing opening portion 19 c 2 through which a screw 41 is penetrated, thereby fixing the brush holder unit 19 and the gear housing 26. And the brush holders 21 and 21 made of metal material such as brass are fixed to the base part 19 c, and two brushes 20 and 20 are disposed in the brush holders 21 and 21 so as to be able to get close to and away from the commutator 15. As shown in FIGS. 4A and 5B, in this invention, two brushes 20 and 20 are located around the rotation center O of the armature 18 at intervals of approximately 90 degrees.

The brush holders 21 are disposed in the vicinity of one of the paired flat surface parts 19 b of the base part 19 c. Fixing claws 21 a of the brush holders 21 are inserted in a brush holder fixing part 19 c 3 formed in the base part 19 c, and the fixing claws 21 a are folded on the back surface side of the base part 19 c, so that the brush holder 21 is fixed to the base part 19 c.

Furthermore, the brush holder unit 19 includes a brush holder guide wall 19 d and a brush terminal connecting part 19 e, and the brush holder guide wall 19 d is formed into a shape approximately the same as the outer shape (elliptical shape) of the base part 19 c and disposed so as to extend at the right angle from the base part 19 c. And the brush terminal connecting part 19 e protrudes from the base part 19 c in a direction opposite to the brush holder guide wall 19 d and at the right angle with respect to the base part 19 c. Furthermore, the brush terminal connecting part 19 e is disposed at a position facing the brushes 20, that is, on the other flat surface part 19 b away from the one flat surface part 19 b where the brushes 20 and 20 are disposed. With this, it is hard to transmit heat generated from the brushes 20 to the brush terminal connecting part 19 e and the control board 29 c electrically connected to the brush terminal connecting part 19 e.

On the base part 19 c, choke coils 22, 22 as noise preventive elements are mounted, and one end of each of the choke coils 22, 22, and a corresponding one of the brushes 20 and 20 are electrically connected via a corresponding one of pigtails 20 a, 20 a. To the other end of each choke coil 22, a female type brush terminal 23 is electrically connected, and the female type brush terminal 23 is electrically connected to a male type terminal 29 g provided to the gear housing cover 29. The female type brush terminal 23 has a tip thereof accommodated in the brush terminal connecting part 19 e, and is exposed from the brush terminal connecting part 19 e so as to be able to electrically connect to the male type terminal 29 g of the gear housing cover 29. When the brush holder unit 19 is mounted on the brush holder accommodating part 26 d, the brush holder guide wall 19 d abuts on an inner wall 26 d 1 of the brush holder accommodating part 26 d, and the brush holder unit 19 is guided to a bottom portion 26 d 2 of the brush holder accommodating part 26 d. Then, the brush holder unit 19 and the gear housing 26 are fixed with the screw 41 penetrating through the fixing opening portion 19 c 2 formed in the base part 19 c.

As shown in FIGS. 2A, 3A, and 4B, the gear housing 26 is formed by die cast molding by using metal material such as aluminum. And the gear housing 26 is formed with a yoke fixing part 26 a, and the yoke fixing part 26 a and the flange shaped fixing part 13 e of the yoke 13 abut on each other, and the yoke 13 is mounted on the gear housing 26 with a plurality of screws 42.

The yoke fixing part 26 a is formed into an elliptical shape with paired curved parts 26 b and paired flat surface parts 26 c being alternately connected so as to match the shape of the flange shaped fixing part 13 e. In the gear housing 26, the brush holder accommodating part 26 d is integrally formed with the yoke fixing part 26 a, and the brush holder unit 19 is accommodated in the brush holder accommodating part 26 d. On the bottom portion 26 d 2 of the brush holder accommodating part 26 d, brush holder abutting parts 26 e each abutting on the fixing claw 21 a of the brush holder 21 are formed so as to protrude from the bottom portion 26 d 2. Heat generated from the brushes 20 and 20 is transmitted from the fixing claws 21 a of the brush holders 21 via the brush holder abutting parts 26 e to the gear housing 26, and is dissipated from the gear housing 26 to the outside.

Furthermore, in the gear housing 26, the speed reduction mechanism accommodating part 26 f in which the worm wheel part 25 a is accommodated is formed so as to be adjacent to the brush holder accommodating part 26 d. In the gear housing 26, the output shaft supporting part 26 g for directly or indirectly supporting the output shaft 24 is formed in a direction opposite to an opening of the speed reduction mechanism accommodating part 26 f.

Furthermore, in the speed reduction mechanism accommodating part 26 f, a cover connecting part 26 h opens. After the brush holder unit 19 described above is accommodated in the brush holder accommodating part 26 d, two male type terminals 29 g which are provided so as to protrude from the bottom surface of the gear housing cover 29 toward the speed reduction mechanism accommodating part 26 f penetrate through the cover connecting part 26 h to be electrically connected to the female type brush terminals 23 of the brush holder unit 19 disposed in the speed reduction mechanism accommodating part 26 f.

The output shaft 24 protruding from the output shaft supporting part 26 g is fixed by an output shaft fixing part (a teeth washer) 27, and to the tip of the output shaft 24, a wiper device fixing part 24 a to which a swinging member 43 such as wiper arm or motor crank is directly or indirectly fixed by a fixing member 44 such as nut is formed, thereby mechanically connecting components forming the wiper device (not shown).

As shown in FIGS. 6 and 7, first heat sinks 26 i as first heat dissipating members for dissipating Joule heat generated by electrical factor, that is, contact resistance between the brushes 20 and 20 and the commutator 15, and frictional heat generated by mechanical factor, that is, sliding movement between the brushes 20 and 20 and the commutator 15, a second heat sink 26 j as a second heat dissipating member for dissipating heat generated from FETs 29 e mounted on the control board, which will be further described below, and a third heat sink 26 k as a third heat dissipating member are formed on an outer peripheral surface of the gear housing 26 positioned at a back surface of the speed reduction mechanism accommodating part 26 f.

The brushes 20 and 20 are disposed in the vicinity of an outer peripheral surface of one of the paired flat surface parts 26 c of the brush holder accommodating part 26 d, and the first heat sinks 26 i protrude from this surface, and are spaced from each other at predetermined intervals in parallel. The first heat sinks 26 i are formed so as to be parallel to a longitudinal direction of the armature shaft 14.

As shown in FIG. 7, in this invention, since two brushes 20 and 20 which are disposed so as to be spaced apart from each other at intervals of approximately 90 degrees are disposed in the vicinity of the first heat sinks 26 i, heat generated from the brushes 20 and 20 is transmitted to the first heat sinks 26 i and dissipated to the outside. And, since the brushes 20 and 20 are disposed at a position away from the control board 29 c with respect to the first heat sinks 26 i, it is easy to transmit heat generated from the brushes to the first heat sinks 26 i, and it is hard to transmit it to the control board 29 c.

Furthermore, as shown in FIG. 5A, between the base part 19 c and the brush holder abutting part 26 e of the gear housing 26, a gel type heat conducting member 28 is disposed. Heat generated from the brushes 20 and 20 is easily transmitted via the heat conducting member 28 to the first heat sinks 26 i.

To an opening of the gear housing 26, the gear housing cover 29 formed into a bottomed shape and formed of insulating material is provided. An open end face of the gear housing 26 and the gear housing cover 29 abut on each other, and the gear housing cover 29 is fixed to the gear housing 26 with the plurality of screws 40.

As shown in FIGS. 3A, 3B, and 4A, the gear housing cover 29 includes a coupler part 29 a, and the coupler part 29 a is provided with a plurality of terminals 29 f. One end of each of the plurality of terminals 29 f is electrically connected to a connector part (not shown) provided to a vehicle, and the other end of each of the plurality of terminals 29 f is electrically connected to the control board 29 c. And the terminals 29 f have intermediate portions thereof which are buried in the gear housing cover 29.

Furthermore, from a bottom portion 29 h of the gear housing cover 29, two male type terminals 29 g protrude, and are electrically connected to the female type brush terminals 23 disposed in the brush holder unit 19. With this configuration, electric power supplied from a power supply of the vehicle is supplied to the motor unit 10 through the plurality of terminals 29 f, the control board 29 c, the male type terminals 29 g, the female type brush terminals 23, the pigtails 20 a, and the brushes 20 and 20.

As shown in FIG. 8, the control board 29 c is mounted on the bottom portion 29 h of the gear housing cover 29 with a plurality of screws, and is accommodated in the speed reduction mechanism accommodating part 26 f of the gear housing 26.

On a surface of the control board 29 c facing the bottom portion 29 h of the gear housing cover, the only Hall IC for absolute position detection 29 d is provided. The Hall IC for absolute position detection 29 d is disposed so as to face the sensor magnet 25 c provided to the base end of the output shaft of the worm wheel part 25 a, and configured to detect the rotating state of the output shaft 24 of the wiper motor 1.

And, based on the rotating state of the output shaft 24 of the wiper motor 1, the control board 29 c is configured to control the rotation of the armature 18 of the motor unit 10.

The control board 29 c is provided with the plurality of FETs 29 e to control electric current flowing through the motor unit 10 with an ON/OFF operation of the FETs 29 e, and to control the rotation of the armature 18 of the motor unit 10 in a forward direction and a reverse direction. Furthermore, on the control board 29 c, a temperature detecting part not shown in the drawing is disposed, thereby detecting the temperature of the control board 29 c.

When load is applied to the wiper motor 1 and the temperature of the control board 29 c detected by the temperature detecting part becomes equal to or higher than a predetermined temperature, based on a signal from the temperature detecting part indicating that the temperature becomes equal to or higher than the predetermined temperature, the control board 29 c causes the rotation numbers to be decreased, and even further, causes the rotation of the armature 18 to stop, thereby achieving protection of the control board 29 c of the wiper motor 1 by the temperature detecting part.

Also, on a surface near the FETs 29 e of the speed reduction mechanism accommodating part 26 f, a FET heat dissipating part 26 m is formed. The FET heat dissipating part 26 m protrudes from the bottom surface of the speed reduction mechanism accommodating part 26 f toward an opening direction, and is formed near a back surface of the control board 29 c to which the FETs 29 e are fixed. On the FET heat dissipating part 26 m, a FET heat dissipating member 30 of a gel type and formed of a material with a high heat conductivity is mounted so as to fill a gap between the control board 29 c and the FET heat dissipating part 26 m. Heat generated from the FETs 29 e is transmitted via the control board 29 c and the FET heat dissipating member 30 to the FET heat dissipating part 26 m, and is dissipated from the second heat sink 26 j and the third heat sink 26 k, formed on the outer peripheral surface of the gear housing 26 to the outside of the gear housing. With this, an increase in temperature of the control board 29 c due to heating of the FETs 29 e can be suppressed. For this reason, the wiper motor 1 can be actuated for a longer time.

When the wiper device is actuated for a long period of time, the brushes 20 and 20, the motor unit 10, and the FETs 29 e generate heat, thereby possibly preventing continuous actuation of the wiper device. For this reason, in the present invention, the second heat sink 26 j and the third heat sink 26 k are further formed near the first heat sinks 26 i on the outer peripheral surface of the gear housing 26 so as to extend outward (on a side opposite to the gear housing cover 29). The plurality of FETs 29 e are disposed near the second heat sink 26 j and the third heat sink 26 k across the control board 29 c. With this, heat generated from the FETs 29 e is dissipated via the control board 29 c from the second heat sink 26 j and the third heat sink 26 k to the outside of the gear housing 26.

As described above, in the above embodiment, a case where the present invention is applied to a wiper motor having connecting lines has been described. However, the present invention is not meant to be restricted to this embodiment, and can be applied to a wiper motor in general, the motor having a brush accommodated in a gear housing formed into an elliptical shape, and a structure in which a heat sink is disposed on an outer peripheral surface of the gear housing in the vicinity of the brush.

Furthermore, although the four-pole wiper motor provided with a four-pole magnet is described as one embodiment of the present invention, the wiper motor may be provided with a cylindrical magnet (ring magnet) polarized so as to have four or more poles.

Furthermore, although the wiper motor having wiper component parts, such as armature and speed reduction mechanism, accommodated in the yoke and gear housing connected to the yoke are disclosed as one embodiment of the present invention, cases in which wiper component parts such as armature and speed reduction mechanism are accommodated may be formed of iron plate in advance, and after the wiper component parts are incorporated in one case, the other case may be mounted on it.

The wiper motor is used as a driving source of a wiper device mounted on a vehicle such as an automobile, and used to wipe out rainwater and others attached onto a windshield by swing the wiper arm.

While the present invention has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this invention may be made without departing from the spirit and scope of the present. 

What is claimed is: 1-4. (canceled)
 5. A wiper motor, comprising: a yoke; a magnet formed with four poles in which different magnetic poles are alternately disposed on an inner peripheral surface of the yoke; an armature including an armature shaft which has one end rotatably supported by a bottom portion of the yoke, a commutator which is fixed to the armature shaft, and a core which is fixed to the armature shaft and around which a winding wire is wound, wherein the armature is rotatably disposed on an inner side of the magnet; two brushes slidably contacting with the commutator, the brushes being disposed so as to be spaced apart from each other at intervals of 90 degrees; a speed reduction mechanism unit having an output shaft for transmitting the rotation of the armature shaft by meshing with a worm formed on the armature shaft; a gear housing connected to the yoke, the gear housing being formed with a speed reduction mechanism accommodating part having accommodated therein the speed reduction mechanism unit, and formed into a bottomed open shape; a gear housing cover covering an opening of the gear housing; a sensor magnet attached to the output shaft; an absolute position detecting sensor disposed so as to face the sensor magnet; and a control board having the absolute position detecting sensor attached thereto, the control board being disposed between the gear housing and the gear housing cover, and configured to control the rotation of the armature shaft by using a signal corresponding to the change of magnetic field generated by the sensor magnet and detected by the absolute position detecting sensor.
 6. The wiper motor according to claim 5, wherein the output shaft is formed with a fixing part to which a swinging member is directly or indirectly fixed.
 7. A wiper motor, comprising: a case; a magnet formed with four poles in which different magnetic poles are alternately disposed on an inner peripheral surface of the case; an armature including an armature shaft which is rotatably supported by the case, a commutator which is fixed to the armature shaft, and a core which is fixed to the armature shaft and around which a winding wire is wound, wherein the armature is rotatably disposed on an inner side of the magnet; two brushes slidably contacting with the commutator, the brushes being disposed so as to be spaced apart from each other at intervals of 90 degrees; a speed reduction mechanism unit accommodated in the case, the speed reduction mechanism unit having an output shaft meshing with a worm formed on the armature shaft to transmit the rotation of the armature shaft; a sensor magnet attached to the output shaft; an absolute position detecting sensor disposed so as to face the sensor magnet; and a control board having the absolute position detecting sensor attached thereto, the control board being accommodated in the case, and configured to control the rotation of the armature shaft by using a signal corresponding to the change of magnetic field generated by the sensor magnet and detected by the absolute position detecting sensor.
 8. The wiper motor according to claim 7, wherein the output shaft is formed with a fixing part to which a swinging member is directly or indirectly fixed. 